My guess would be that one end of the spring should sit in position (1) in enclosed picture, this to put tension to the belt. The whole package with drive axis and gear box (I just bought this new due to gear box failure) can move with the axis according to my purple arrow, i.e. the spring should likely put up tension on the whole package, but I don't get it where I should hook up the other/lower end of the tension spring, there is no obvious attachment spot.
